1. Field of the Invention
The present invention relates to a blended electrical/friction braking system of an electric motor powered vehicle and, more particularly, to a system which monitors a regenerative/dynamic braking effort of the electric motor and which operates the friction brake of the vehicle as a function thereof.
2. Background Art
An electrically powered vehicle, such as an electrically powered mass transit vehicle, typically includes an AC or DC electric motor for propelling the vehicle along a path or running rails. During acceleration or constant speed operation of the vehicle, electrical power is controllably supplied to the electric motor. When it is desired to brake the vehicle, the momentum of the vehicle can be utilized to drive the electric motor as a generator for generating electric power which is supplied for use by other electrical/electronic devices and/or for storage in a storage device, such as a battery or capacitor, or for dissipation by a suitable load. The use of the electric motor as a generator to convert the momentum of the vehicle into electric power for such use and/or storage is commonly known as regenerative braking. The use of the electric motor as a generator to convert the momentum of the vehicle into electric power for dissipation by a load is commonly known as dynamic braking. Hereinafter, phrases such as xe2x80x9celectrical brakingxe2x80x9d, xe2x80x9celectric brakingxe2x80x9d, xe2x80x9celectrically brakingxe2x80x9d, xe2x80x9celectrically brakexe2x80x9d and the like, are utilized to refer to driving the xe2x80x9celectric motor in a dynamic braking mode and/or a regenerative braking mode.
Such a vehicle would also include a friction brake which is utilized in a blended manner with the electric motor to brake the wheels of the vehicle in a manner known in the art. In operation, the electric motor is utilized for electrically braking the vehicle at higher speeds where the electric motor can be used more effectively and the friction brake is utilized to brake the vehicle at lower speeds where the electric motor is less effective. Blended electrical/friction braking systems are well-known in the art.
A problem with such blended electrical/friction braking systems, however, is that if the actual extent of electric braking does not correspond to the requested/expected extent of electric braking, no mechanism exists for detecting this lack of correspondence and for causing the friction braking to assume the overall braking effort of the vehicle.
It is, therefore, an object of the present invention to provide a blended electrical/friction braking system having a brake feedback monitor for monitoring a difference between a requested electric braking effort of an electric motor of a vehicle and the actual electric braking effort of the motor and for causing a friction brake of the vehicle to assume the entire braking effort if the difference exceeds a predetermined difference. Still other objects of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.
Accordingly, we have invented a blended electrical/friction braking system for use in a vehicle having an electric motor which can be operated to electrically brake one or more wheels of the vehicle and a friction brake for friction braking one or more wheels of the vehicle. The braking system includes a brake controller for monitoring a brake effort request and for allotting the brake effort request between a first brake effort request corresponding to a desired amount of electrical braking effort to be supplied by the electric motor during electric braking and a second brake effort request corresponding to a desired amount of friction braking effort to be supplied by the friction brake. A drive control unit produces from the first brake effort request a first signal corresponding thereto and supplies the first signal to the brake controller. One or more sensors sense one or more electrical conditions of the electric motor during electrical braking. A brake feedback monitor monitors the first signal, converts the one or more sensed electrical conditions into a second signal corresponding thereto, compares the first signal and the second signal and terminates receipt of the first signal by the brake controller in response to a difference between the first signal and the second signal exceeding a predetermined difference. The brake controller responds to the termination of the first signal thereat by allotting the incoming brake effort request entirely to the second brake effort request. The one or more sensed electrical conditions of the electric motor can include voltage(s), current(s) and/or phase angle(s) therebetween.
The brake feedback monitor can include a processor and a relay connected to the processor to be controlled thereby. The relay has a contact in a path of the first signal between the drive control unit and the brake controller. The processor controls the contact so that (i) the brake controller receives the first signal when the difference between the first signal and the second signal does not exceed the predetermined difference and (ii) the brake controller does not receive the first signal when the difference between the first signal and the second signal exceeds the predetermined difference.
The brake feedback monitor can also include a pair of relays connected in series in the path of the first signal between the drive control unit and the brake controller and a pair of processors each connected to control the contacts of the pair of relays and connected to sense the first signal on the path between the pair of relays and the brake controller. One processor determines the second signal from the one or more sensed electrical condition and supplies the second signal to the other processor. Each processor can determine whether the difference between the first signal and the second signal exceeds the predetermined difference. In response to determining the difference exceeds the predetermined difference, each processor can signal one relay to change state thereby terminating receipt of the first signal by the brake controller.
Each relay can include a status output connected to one of the processors for supplying thereto an indication of the state of the contact of the relay. Each processor can signal the other relay to change state if the status output of the one relay does not indicate that the one relay is in a state that terminates receipt of the first signal by the brake controller. Moreover, each processor, in response to detecting the first signal after signaling the one relay to change state, can signal the other relay to change state. Preferably, the first and/or second signals are pulse width modulated signals.
We have also invented a brake feedback monitor for monitoring a first signal corresponding to an electric brake effort request of an electric motor of an electrically powered vehicle, for monitoring one or more electrical conditions of the electric motor in response to the electric brake effort request, and for selectively supplying/terminating the first signal to/from a brake controller as a function of the first signal and the one or more electrical conditions.
The brake feedback monitor can include a first relay having a contact in series with a path of the first signal and a first control input for receiving a first control signal which controls the state of the first relay contact. A first processor can be connected to monitor the first signal and to monitor the one or more electrical conditions. The first processor can convert the monitored one or more electrical conditions into a second signal and can determine if a difference between the first signal and the second signal exceeds a predetermined difference. The first processor can also supply the first control signal to the first relay for causing the first relay contact to assume one state when the difference does not exceed the predetermined difference and for causing the first relay contact to assume another state when the difference exceeds the predetermined difference.
The brake feedback monitor can also include a second relay having a contact in series with the path of the first signal and a first control input for receiving a second control signal which controls the state of the second relay contact. A second processor can be connected for monitoring the first signal and for receiving the second signal from the first processor. The second processor can also determine if a difference between the first signal and the second signal exceeds a predetermined difference. The second processor can supply the second control signal for causing the second relay contact to assume one state when the difference does not exceed the predetermined difference and for causing the second relay contact to assume another state when the difference exceeds the predetermined difference. Preferably, the one state is a closed state and the other state is the opened state.
The second relay can have a second control input for receiving a third control signal which controls the state of the second relay contact. The first relay can have a second control input for receiving a fourth control signal which controls the state of the first relay contact.
In response to detecting the presence of the first signal after supplying the first control signal for causing the first relay contact to assume its opened state, the first processor can supply the third control signal to the second relay for causing the second relay contact to assume its opened state. Similarly, in response to detecting the presence of the first signal after supplying the second control signal for causing the second relay contact to assume its opened state, the second processor can supply the fourth control signal to the first relay for causing the first relay contact to assume its opened state.
Each relay can also include a status output which provides a status of the state of the contact thereof. The status output of the first relay is connected to the first processor and the status output of the second relay is connected to the second processor. After supplying the first control signal for causing the first relay contact to assume its opened state and in response to detecting via the status output of the first relay that the first relay contact is in its closed state, the first processor can supply the third control signal to the second relay for causing the second relay contact to assume its opened state. Similarly, after supplying the second control signal for causing the second relay contact to assume its opened state and in response to detecting via the status output of the second relay that the second relay contact is in its closed state, the second processor can supply the fourth control signal to the first relay for causing the first relay contact to assume its opened state.
Lastly, we have invented a method of braking an electric motor powered vehicle. The method includes allotting a brake effort request between an electric brake effort request and a friction brake effort request. The electric brake effort request is converted into a first signal which is monitored along with one or more electrical conditions of the electric motor in response to the electric brake effort request. A feedback path for the first signal is selectively opened/closed as a function of the first signal and the one or more electrical conditions. In response to opening the feedback path, the incoming brake effort request is allotted entirely to the friction brake effort request.
The step of selectively opening/closing the feedback path can include the steps of providing a pair of relays with each relay having a contact disposed in series with the feedback path and a status output which provides a status of the state of the contact thereof. One relay can be signaled to open its contact as a function of the first signal and the one or more electrical conditions. Thereafter, in response to detecting the presence of the first signal downstream in the feedback path from the one relay and/or the status output of the one relay that its contact is closed, the other relay can be signaled to open its contact.
The one or more electrical conditions can be converted into a second signal and a difference between the first signal and the second signal can be determined. The feedback path can be closed when the difference does not exceed a predetermined difference and the feedback path can be opened when the difference exceeds the predetermined difference.